In lambda control of a motor vehicle, that is, when setting a suitable combustion air ratio for a motor vehicle, which is done mass-based using the oxygen storage capacity (OSC), balancing of the current degree of oxygen filling of the catalytic converter is of special importance. For balancing of oxygen entry and oxygen discharge generally a formula is used which is based on the idea that the catalytic converter should be able to accept or release the entire oxygen excess or the entire oxygen deficiency in the exhaust gas if the oxygen storage reservoir of the catalytic converter is not completely filled or is completely empty.
But it is problematic in this type of control that catalytic converters which, for example, during an acceleration phase, are exposed to high masses of exhaust gas, show nitrogen oxide breakthroughs (NOx breakthroughs) even though the average charging of the oxygen storage reservoir has been reduced to values of less than 50%. The reason for this is that, as a result of the aforementioned balancing approach according to which once the theoretical filling state of the catalytic converter has been brought to the desired value of less than 50%, a lambda value of 1 is again set, that is, a stoichiometric ratio at which ratio nitrogen oxide breakthroughs which can be considered to be disadvantageous appear in an exhaust gas test.
The object of the invention is thus to devise a method which has been improved in this respect.